US20210218060A1 - Electrolyte composition and use thereof in lithium-ion batteries - Google Patents

Electrolyte composition and use thereof in lithium-ion batteries Download PDF

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US20210218060A1
US20210218060A1 US16/492,227 US201816492227A US2021218060A1 US 20210218060 A1 US20210218060 A1 US 20210218060A1 US 201816492227 A US201816492227 A US 201816492227A US 2021218060 A1 US2021218060 A1 US 2021218060A1
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mol
equal
lithium
composition
carbonate
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US16/492,227
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Sabrina PAILLET
Gregory Schmidt
Ian Cayrefourcq
Julie HAMEL-PÂQUET
Ali DARWICHE
Gabriel Girard
Joël Fréchette
Sébastien LADOUCEUR
Abdelbast Guerfi
Karim Zaghib
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Hydro Quebec
Arkema France SA
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Hydro Quebec
Arkema France SA
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Priority claimed from CA2960489A external-priority patent/CA2960489A1/en
Priority claimed from FR1751971A external-priority patent/FR3063836B1/en
Application filed by Hydro Quebec, Arkema France SA filed Critical Hydro Quebec
Assigned to HYDRO-QUéBEC, ARKEMA FRANCE reassignment HYDRO-QUéBEC ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SCHMIDT, GREGORY, LADOUCEUR, Sébastien, DARWICHE, Ali, FRÉCHETTE, Joël, GIRARD, GABRIEL, GUERFI, ABDELBAST, HAMEL-PÂQUET, Julie, ZAGHIB, KARIM, CAYREFOURCQ, IAN, Paillet, Sabrina
Publication of US20210218060A1 publication Critical patent/US20210218060A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
    • C07D233/54—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members
    • C07D233/66—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
    • C07D233/90—Carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
    • C07D233/54—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members
    • C07D233/66—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
    • C07D233/91—Nitro radicals
    • C07D233/92—Nitro radicals attached in position 4 or 5
    • C07D233/93—Nitro radicals attached in position 4 or 5 with hydrocarbon radicals, substituted by halogen atoms, attached to other ring members
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • H01M2300/004—Three solvents
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of batteries, more particularly to the field of electrolyte compositions comprising lithium ions.
  • a lithium-ion battery comprises at least a negative electrode (anode), a positive electrode (cathode), a separator and an electrolyte.
  • the electrolyte generally consists of a lithium salt dissolved in a solvent which is usually a mixture of organic carbonates, in order to have a good compromise between viscosity and dielectric constant. Additives can then be added to improve stability of the electrolyte salts.
  • LiPF 6 lithium hexafluorophosphate
  • HF hydrofluoric acid
  • LiTFSI lithium bis(trifluoromethanesulfonyl)imide
  • LiFSI lithium bis(fluorosulfonyl)imide
  • the present application relates to an electrolyte composition
  • an electrolyte composition comprising lithium hexafluorophosphate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate, at least one solvent, and at least one electrolytic additive, said composition comprising:
  • the content of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate is less than or equal to 0.2 mol/L, in particular less than or equal to 0.1 mol/L, preferably less than or equal to 0.08 mol/L, more preferably less than or equal to 0.05 mol/L, relative to the total volume of composition.
  • the composition solvent is selected from the group consisting of ethers, carbonic acid esters, cyclic carbonate esters, aliphatic carboxylic acid esters, aromatic carboxylic acid esters, phosphoric acid esters, sulfite esters, nitriles, amides, alcohols, sulfoxides, sulfolane, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1,H)-pyrimidinone, 3-methyl-2-oxazolidinone, and mixtures thereof.
  • the solvent is selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate, methyl phenyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, and mixtures thereof.
  • the solvent may also be selected from ethylene carbonate, diethyl carbonate, and mixtures thereof.
  • the electrolytic additive is selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, allyl ethyl carbonate, vinyl acetate, divinyl adipate, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonates, vinyl containing silane compounds, 2-cyanofurane and mixtures thereof, the electrolytic additive preferably being fluoroethylene carbonate.
  • the content of electrolytic additive is comprised between 0.1% and 9%, preferably between 0.5% and 4% by weight relative to the total combined weight of solvent(s) and additive.
  • the concentration of lithium hexafluorophosphate in the electrolyte composition is greater than or equal to 0.80 mol/L and less than 1 mol/L, preferably comprised between 0.80 and less than 1 mol/L, particularly between 0.90 and 0.99 mol/L, and for example comprised between 0.95 mol/L and 0.99 mol/L.
  • the lithium hexafluorophosphate concentration is of about 0.95 mol/L
  • the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentration is of about 0.05 mol/L, relative to the total volume of composition.
  • the present application also relates to the use of a composition as defined herein, in a Li-ion battery, particularly in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C.
  • a composition as defined herein for example, use is made in mobile devices, for instance mobile phones, cameras, tablets or laptops, in electric vehicles, or in the storage of renewable energy.
  • Another embodiment comprises the use of a composition as defined in the present application for improving life duration of a Li-ion battery; and/or improving cycling stability of a Li-ion battery; and/or reducing irreversible capacity of a Li-ion battery; particularly in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C.
  • Another aspect of the present application relates to an electrochemical cell comprising a negative electrode, a positive electrode, and an electrolyte composition as defined herein, interposed between the negative electrode and the positive electrode.
  • the negative electrode of the electrochemical cell comprises graphite, carbon fibers, carbon black, lithium, or a mixture thereof, the negative electrode preferably comprising graphite.
  • the electrochemical cell as described herein may have a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles relative to the first cycle, for a charge comprised between a voltage V low comprised between 2.0 and 3.0 volts versus Li + /Li 0 , and a voltage V high comprised between 3.8 and 4.2 volts versus Li + /Li 0 , at a temperature of 25° C., and at a charge and discharge C rate.
  • the voltage V low is equal to 2.8 volts and the voltage V high is equal to 4.2 volts
  • the electrochemical cell has a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage V low between 2.0 and 3.0 volts versus Li + /Li 0 , and a voltage V high between 3.8 and 4.2 volts versus Li + /Li 0 , at a temperature of 25° C., and at a charge and discharge C rate, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO 4 .
  • the voltage V low is equal to 2 volts and the voltage V high is equal to 4 volts.
  • charging is followed by the application of a constant voltage of 4V for 30 minutes.
  • charging is not followed by the application of a constant voltage and the capacity retention is greater than or equal to 80% relative to the first cycle after at least 800 charge/discharge cycles.
  • this application also relates to a battery comprising at least one electrochemical cell as described in the present application.
  • Another aspect relates to the use of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate in an electrolyte composition comprising lithium hexafluorophosphate and at least one electrolytic additive for:
  • composition being such that:
  • FIG. 1 shows the variation in discharge capacity as a function of the number of cycles performed at 45° C. as described in Example 1.
  • FIG. 2 shows the variation in discharge capacity as a function of the number of cycles performed at 60° C. as described in Example 2.
  • FIG. 3 shows the variation in discharge capacity as a function of the number of cycles performed at 25° C. as described in Example 3.
  • FIG. 4 shows the variation in discharge capacity as a function of the number of cycles performed at 40° C. as described in Example 3.
  • FIG. 5 shows the variation in discharge capacity as a function of the number of cycles performed at 60° C. as described in Example 3.
  • the present application describes electrolyte compositions comprising specific concentration and ratio of two lithium salts, a solvent (that may be a mixture of solvents) and an electrolytic additive. More specifically, the electrolyte composition comprises lithium hexafluorophosphate (LiPF 6 ), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate (LiTDI), at least one solvent, and at least one electrolytic additive.
  • the electrolyte composition as described herein comprises:
  • the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate content is less than or equal to 0.25 mol/L, or less than or equal to 0.2 mol/L, particularly less than or equal to 0.15 mol/L, or less than or equal to 0.1 mol/L, preferably less than or equal to 0.08 mol/L, preferably less than or equal to 0.05 mol/L, relative to the total volume of composition.
  • the lithium hexafluorophosphate concentration in the electrolyte composition may be greater than or equal to 0.80 mol/L and less than 1 mol/L, preferably comprised between 0.80 and less than 1 mol/L, particularly between 0.90 and 0.99 mol/L, and for example comprised between 0.95 mol/L and 0.99 mol/L, relative to the total volume of composition.
  • lithium hexafluorophosphate and lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentrations in the electrolyte composition comprise:
  • the electrolyte composition as described in the present application comprises 0.95 mol/L of LiPF 6 and 0.05 mol/L of LiTDI, relative to the total volume of composition.
  • the solvent is non aqueous (organic).
  • the composition solvent may be selected from the group consisting of ethers, carbonic acid esters, cyclic carbonate esters, aliphatic carboxylic acid esters, aromatic carboxylic acid esters, phosphoric acid esters, sulfite esters, nitriles, amides, alcohols, sulfoxides, sulfolane, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1,H)-pyrimidinone, 3-methyl-2-oxazolidinone, or one of their mixtures.
  • ethers mention may be made of linear or cyclic ethers such as, for example, dimethoxyethane (DME), methyl ethers of oligoethylene glycols of 2 to 5 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and their mixtures.
  • DME dimethoxyethane
  • methyl ethers of oligoethylene glycols of 2 to 5 oxyethylene units dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and their mixtures.
  • nitriles mention may be made, for example, of acetonitrile, pyruvonitrile, propionitrile, methoxypropionitrile, dimethylaminopropionitrile, butyronitrile, isobutyronitrile, valeronitrile, pivalonitrile, isovaleronitrile, glutaronitrile, methoxyglutaronitrile, 2-methylglutaronitrile, 3-methylglutaronitrile, adiponitrile, malononitrile, and their mixtures.
  • solvents also include those selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate, methyl phenyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, and their mixtures.
  • the solvent may also be selected from ethylene carbonate (EC-CAS N° 96-49-1), diethyl carbonate (DEC-CAS N° 105-58-8), and their mixtures.
  • the solvent is an ethylene carbonate:diethyl carbonate mixture in a ratio of between 1:99 and 99:1, preferably between 10:90 and 90:10, more preferably between 40:60 and 60:40.
  • electrolytic additive examples include fluoroethylene carbonate (FEC), vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, allyl ethyl carbonate, vinyl acetate, divinyl adipate, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonates, vinyl containing silane compounds, 2-cyanofurane and their mixtures, the electrolytic additive preferably being fluoroethylene carbonate (FEC).
  • the electrolytic additive content may be comprised between 0.1% and 9%, preferably between 0.5% and 4%, by weight relative to the combined “solvent(s)+additive” total weight.
  • the electrolytic additive content in the electrolyte composition is less than or equal to 2% by weight relative to the combined “solvent(s)+additive” total weight.
  • the present electrolyte composition is selected from one of the following compositions (LiPF 6 and LiTDI concentrations being expressed relative to the total composition volume and the additive content relative to the combined “solvent(s)+additive” total weight):
  • the electrolyte composition may be prepared by dissolving, preferably with stirring, the salts in the appropriate proportions of solvent(s) comprising the electrolytic additive.
  • the electrolyte composition may be prepared by dissolving, preferably with stirring, the salts and the electrolytic additive in appropriate proportions of solvent(s).
  • an electrolyte composition of the present application in a Li-ion battery is also contemplated, in particular in a temperature range of higher than or equal to 25° C., preferably of between 25° C. and 65° C., advantageously between 40° C. and 60° C.
  • use is made in mobile devices, for instance mobile phones, cameras, tablets or laptops, in electric vehicles, or for the storage of renewable energy.
  • the present application thus also relates to an electrochemical cell comprising a negative electrode, a positive electrode, and an electrolyte composition as defined herein, interposed between the negative electrode and the positive electrode.
  • the electrochemical cell may also further comprise a separator in which the electrolyte composition of the present application is impregnated.
  • the present application also contemplates a battery comprising at least one electrochemical cell defined in this application.
  • the battery comprises several of these electrochemical cells, said cells can be assembled serially and/or in parallel.
  • negative electrode the electrode which acts as anode, when the battery delivers current (i.e. when in discharge process) and which acts as cathode when the battery is in charging process.
  • the negative electrode typically comprises an electrochemically active material, optionally an electronically conductive material, and optionally a binder.
  • electrochemically active material means a material capable of reversibly inserting ions, without irreversibly damaging their structure.
  • electronically conductive material is meant a material capable of conducting electrons.
  • the battery negative electrode may comprise as electrochemically active material, graphite, carbon fibers, carbon black, or a mixture thereof, the negative electrode preferably comprising graphite.
  • the negative electrode may also comprise lithium, which may then consist of a metallic lithium film or of an alloy comprising lithium.
  • a negative electrode example comprises an active lithium film prepared by rolling a lithium foil between rolls.
  • positive electrode the electrode which acts as a cathode when the battery delivers current (i.e. when in discharge process) and which acts as the anode when the battery is in charging process.
  • the positive electrode usually comprises an electrochemically active material, optionally an electronically conductive material, and optionally a binder.
  • the positive electrode material may also comprise an electronically conductive material such as a carbon source, including, for example, carbon black, Ketjen® carbon, Shawinigan carbon, graphite, graphene, carbon nanotubes, carbon fibers (such as vapor grown carbon fibers (VGCF)), non-powdery carbon obtained by carbonizing an organic precursor, or a combination of at least two thereof.
  • a carbon source including, for example, carbon black, Ketjen® carbon, Shawinigan carbon, graphite, graphene, carbon nanotubes, carbon fibers (such as vapor grown carbon fibers (VGCF)), non-powdery carbon obtained by carbonizing an organic precursor, or a combination of at least two thereof.
  • Other additives may also be present in the positive electrode material, such as lithium salts or inorganic particles of ceramic or glass type, or other compatible active materials (for example, sulfur).
  • the positive electrode material may also comprise a binder.
  • binders include linear, branched and/or crosslinked polyether polymer binders (e.g., polymers based on poly(ethylene oxide) (PEO), or poly(propylene oxide) (PPO) or a mixture of both (or a EO/PO copolymer), and optionally comprising crosslinkable units), water soluble binders (such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber)), or fluorinated polymer type binders (such as PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and their combinations).
  • Some binders, such as those soluble in water, may also include an additive such as CMC (carboxymethylcellulose).
  • the electrochemical cell comprises a negative electrode containing graphite, a positive electrode containing LiFePO 4 (LFP) and a mixture of carbon black with carbon fibers and/or carbon nanotubes, and an electrolyte composition as defined herein, interposed between the negative electrode and positive electrode, the composition preferably being selected from any of the following compositions (LiPF 6 and LiTDI concentrations being expressed relative to the total volume of composition and the additive content expressed relative to the “solvent(s)+additive” total combined weight):
  • the electrochemical cell as described herein may have a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage V low between 2.0 and 3.0 volts versus Li + /Li 0 , and a voltage V high between 3.8 and 4.2 volts versus Li + /Li 0 , at a temperature of 45° C., and at a charge and discharge C rate.
  • the voltage V low may be of 2.8 volts and the voltage V high is of 4.2 volts
  • the electrochemical cell as described herein may have a capacity retention greater than or equal to 80% after at least 60 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage V low between 2.0 and 3.0 volts versus Li + /Li 0 , and a voltage V high between 3.8 and 4.2 volts versus Li + /Li 0 , at a temperature of 60° C., and at a charge and discharge C/4 rate, charging being optionally followed by the application of a constant voltage of 4.2V for 1 h.
  • the voltage V low is of 2.8 volts and the voltage V high is of 4.2 volts
  • charging is followed by the application of a constant voltage as described.
  • the electrochemical cell of the present technology has a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage V low of between 2.0 and 3.0 volts versus Li + /Li 0 , and a voltage V high of between 3.8 and 4.2 volts versus Li + /Li 0 , at a temperature of 25° C., and at a charge and discharge rate of C, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO 4 .
  • the voltage V low may be equal to 2 volts and the voltage V high is of 4 volts.
  • charging is followed by the application of a constant voltage as described.
  • the electrochemical cell of the present technology may also have a capacity retention greater than or equal to 80% after at least 200 charge/discharge cycles relative to the first cycle, for a charge comprised between a voltage V low between 2.0 and 3.0 volts versus Li + /Li 0 , and a voltage V high between 3.8 and 4.2 volts versus Li + /Li 0 , at a temperature of 40° C., and at a charge and discharge C rate, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO 4 .
  • the voltage V low is equal to 2 volts and the voltage V high is of 4 volts.
  • charging is followed by the application of a constant voltage as described.
  • the electrochemical cell of the present technology may have a capacity retention greater than or equal to 80% after at least 100 charge/discharge cycles relative to the first cycle, for a charge comprised between a voltage V low between 2.0 and 3.0 volts versus Li + /Li 0 , and a voltage V high between 3.8 and 4.2 volts versus Li + /Li 0 , at a temperature of 60° C., and at a charge and discharge C rate, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO 4 .
  • the voltage V low is equal to 2 volts and the voltage V high is of 4 volts.
  • charging is followed by the application of a constant voltage as described.
  • the present application also relates to the use of the electrolyte composition as described herein for:
  • Another aspect relates to the use of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate in an electrolyte composition comprising lithium hexafluorophosphate and at least one electrolytic additive for:
  • composition being such that:
  • the use of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate in an electrolyte composition as herein described and comprising lithium hexafluorophosphate and at least one electrolytic additive makes it possible to improve the life duration of a Li-ion battery; and/or to improve the stability to cycling of a Li-ion battery; and/or to reduce the irreversible capacity of a Li-ion battery.
  • This improvement may occur especially in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C.
  • the presence of LiTDI in the electrolyte composition makes it possible to increase the life of the battery (80% loss of initial capacity) by at least 1.5-fold, or at least 2-fold, compared to a battery without LiTDI used in the same conditions.
  • the battery life is multiplied by at least 1.5, or at least 2, or multiplied by a number within the range of from 1.5 to 8, or from 2 to 7.
  • between x and y means an interval in which the x and y terminals are included.
  • the range “between 1 and 4%” namely includes the values 1 and 4%.
  • the first example carried out consists in dissolving, at room temperature, a salt mixture containing LiPF 6 and LiTDI (or LiPF 6 alone as a reference) at a total concentration of 1 mol/L, in a mixture of three carbonates: ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in EC/DEC/FEC weight proportions of: 36.84%, 61.16% and 2% respectively.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluoroethylene carbonate
  • the second example carried out consists in dissolving at room temperature a salt mixture containing LiPF 6 and LiTDI (or LiPF 6 alone for the reference) at a total concentration of 1 mol/L, in a mixture of three carbonates: ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in weight proportions of 36.84%, 61.16% and 2% respectively.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluoroethylene carbonate
  • a salt mixture containing LiPF 6 and LiTDI (or LiPF 6 alone for the reference) is dissolved at a total concentration of 1 mol/L in a mixture of three carbonates: ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in weight proportions of 36.84%, 61.16% and 2% respectively.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluoroethylene carbonate
  • the electronic conductor used is a mixture of carbon black with either carbon fibers or nanotubes.
  • the system's cycling terminals are 2-4V. After a slow rate (C/24) formation at room temperature, the mixtures were evaluated at 25, 40 and 60° C. with a C charge followed by application of a constant voltage at 4 V for 30 minutes, and then a C discharge. Results obtained are presented in FIGS. 3, 4 and 5 respectively (results shown for cells comprising 0.05 mol/L of LiTDI).
  • the addition of LiTDI at only 0.05 mol/L makes it possible to multiply by 3.2 the life of the battery with carbon nanotubes as electronic conductor and by 2.5 with the carbon fibers.
  • the improvement in cyclability is more pronounced in the presence of carbon nanotubes where the battery life is increased by 4.2 times by adding 0.2 mol/L of LiTDI.
  • the addition of 0.05 mol/L of LiTDI is sufficient to improve the cycle life of a few tens of cycles, whether with VGCF or CNT electronic conductors.
  • LiTDI from 0.05 mol/L
  • the series of tests carried out also demonstrates the good resistance in abusive cycling (application of constant voltage at the end of charging) of the tested electrolytes when containing LiTDI (from 0.05 mol/L).
  • the tests carried out at room temperature on the LFP/graphite system further demonstrate the resistance to abusive cycling (no temperature effect) of electrolytes containing LiTDI, whether with VGCF or CNT type electronic conductors; the life of the battery being multiplied by 2.5 or 3.2 times.

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Abstract

Electrolyte compositions comprising lithium hexafluorophosphate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate, a solvent, and at least one electrolytic additive, are herein described. The present application also describes the use if these electrolyte compositions in batteries, e.g. within a temperature range higher than or equal to 25° C.

Description

    RELATED APPLICATIONS
  • The present application claims priority under applicable law to Canadian patent application No. 2 960 489 filed on Mar. 10, 2017 and to French patent application No. 17 51971 also filed on Mar. 10, 2017, the content of which is incorporated herein by reference in its entirety for all purposes.
    • TECHNICAL FIELD
  • The present application relates to the field of batteries, more particularly to the field of electrolyte compositions comprising lithium ions.
    • TECHNICAL BACKGROUND
  • A lithium-ion battery comprises at least a negative electrode (anode), a positive electrode (cathode), a separator and an electrolyte. The electrolyte generally consists of a lithium salt dissolved in a solvent which is usually a mixture of organic carbonates, in order to have a good compromise between viscosity and dielectric constant. Additives can then be added to improve stability of the electrolyte salts.
  • Among the most used salts is LiPF6 (lithium hexafluorophosphate), which possesses many of the required qualities but has the disadvantage of degrading to form hydrofluoric acid (HF) by reacting with water. The formed HF can cause a dissolution of the cathode material. The reaction of LiPF6 with residual water thus affects the longevity of the battery and can cause safety problems, especially when lithium-ion batteries are used in private vehicles.
  • Other salts, such as LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (lithium bis(fluorosulfonyl)imide), have thus been developed. These salts show little or no spontaneous decomposition and are more stable to hydrolysis than LiPF6. Nevertheless, LiTFSI has the disadvantage of being corrosive for current collectors, particularly those in aluminum.
  • In the field of batteries, there is an ongoing need for developing electrolyte compositions for improving battery performance, such as its durability, its cycling stability, and/or the reduction of its irreversible capacity.
    • SUMMARY
  • The present application relates to an electrolyte composition comprising lithium hexafluorophosphate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate, at least one solvent, and at least one electrolytic additive, said composition comprising:
      • a total concentration of lithium hexafluorophosphate and lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate of less than or equal to 1 mol/L relative to the total volume of composition, and
      • a concentration of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate of less than or equal to 0.3 mol/L relative to the total volume of composition.
  • According to one embodiment, the content of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate is less than or equal to 0.2 mol/L, in particular less than or equal to 0.1 mol/L, preferably less than or equal to 0.08 mol/L, more preferably less than or equal to 0.05 mol/L, relative to the total volume of composition.
  • According to another embodiment, the composition solvent is selected from the group consisting of ethers, carbonic acid esters, cyclic carbonate esters, aliphatic carboxylic acid esters, aromatic carboxylic acid esters, phosphoric acid esters, sulfite esters, nitriles, amides, alcohols, sulfoxides, sulfolane, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1,H)-pyrimidinone, 3-methyl-2-oxazolidinone, and mixtures thereof. For example, the solvent is selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate, methyl phenyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, and mixtures thereof. The solvent may also be selected from ethylene carbonate, diethyl carbonate, and mixtures thereof.
  • In another embodiment, the electrolytic additive is selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, allyl ethyl carbonate, vinyl acetate, divinyl adipate, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonates, vinyl containing silane compounds, 2-cyanofurane and mixtures thereof, the electrolytic additive preferably being fluoroethylene carbonate. For instance, the content of electrolytic additive is comprised between 0.1% and 9%, preferably between 0.5% and 4% by weight relative to the total combined weight of solvent(s) and additive.
  • In an embodiment, the concentration of lithium hexafluorophosphate in the electrolyte composition is greater than or equal to 0.80 mol/L and less than 1 mol/L, preferably comprised between 0.80 and less than 1 mol/L, particularly between 0.90 and 0.99 mol/L, and for example comprised between 0.95 mol/L and 0.99 mol/L. For instance, the lithium hexafluorophosphate concentration is of about 0.95 mol/L, and the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentration is of about 0.05 mol/L, relative to the total volume of composition.
  • The present application also relates to the use of a composition as defined herein, in a Li-ion battery, particularly in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C. For example, use is made in mobile devices, for instance mobile phones, cameras, tablets or laptops, in electric vehicles, or in the storage of renewable energy. Another embodiment comprises the use of a composition as defined in the present application for improving life duration of a Li-ion battery; and/or improving cycling stability of a Li-ion battery; and/or reducing irreversible capacity of a Li-ion battery; particularly in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C.
  • Another aspect of the present application relates to an electrochemical cell comprising a negative electrode, a positive electrode, and an electrolyte composition as defined herein, interposed between the negative electrode and the positive electrode.
  • In one embodiment, the negative electrode of the electrochemical cell comprises graphite, carbon fibers, carbon black, lithium, or a mixture thereof, the negative electrode preferably comprising graphite.
  • In another embodiment, the electrochemical cell positive electrode comprises LiCoO2, LiFePO4 (LFP), LiMnxCoyNizO2 (NMC, where x+y+z=1), LiFePO4F, LiFeSO4F, LiNiCoAlO2 or a mixture thereof, the positive electrode preferably comprising LiFePO4 or LiMnxCoyNizO2 (where x+y+z=1).
  • For example, the electrochemical cell as described herein may have a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles relative to the first cycle, for a charge comprised between a voltage Vlow comprised between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh comprised between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 25° C., and at a charge and discharge C rate. For instance, the voltage Vlow is equal to 2.8 volts and the voltage Vhigh is equal to 4.2 volts, the positive electrode preferably comprising LiCoO2, LiMnxCoyNizO2 (with x+y+z=1), LiFePO4F, LiFeSO4F, LiNiCoAlO2 and mixtures thereof.
  • According to another example, the electrochemical cell has a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage Vlow between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 25° C., and at a charge and discharge C rate, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO4. According to an example, the voltage Vlow is equal to 2 volts and the voltage Vhigh is equal to 4 volts. According to an embodiment, charging is followed by the application of a constant voltage of 4V for 30 minutes. According to another embodiment, charging is not followed by the application of a constant voltage and the capacity retention is greater than or equal to 80% relative to the first cycle after at least 800 charge/discharge cycles.
  • According to another aspect, this application also relates to a battery comprising at least one electrochemical cell as described in the present application.
  • Another aspect relates to the use of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate in an electrolyte composition comprising lithium hexafluorophosphate and at least one electrolytic additive for:
      • improving a Li-ion battery life; and/or
      • improving a Li-ion battery cycling stability; and/or
      • reducing a Li-ion battery irreversible capacity;
  • especially in a temperature range greater than or equal to 25° C., preferably between 25° C. and 65° C., advantageously between 40° C. and 60° C.;
  • the composition being such that:
      • the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate and lithium hexafluorophosphate total concentration is less than or equal to 1 mol/L relative to the total volume of composition; and
      • the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentration is less than or equal to 0.3 mol/L, preferably less than or equal to 0.05 mol/L, relative to the total volume of composition.
    BRIEF DESCRIPTION OF THE FIGURES
  • FIG. 1 shows the variation in discharge capacity as a function of the number of cycles performed at 45° C. as described in Example 1.
  • FIG. 2 shows the variation in discharge capacity as a function of the number of cycles performed at 60° C. as described in Example 2.
  • FIG. 3 shows the variation in discharge capacity as a function of the number of cycles performed at 25° C. as described in Example 3.
  • FIG. 4 shows the variation in discharge capacity as a function of the number of cycles performed at 40° C. as described in Example 3.
  • FIG. 5 shows the variation in discharge capacity as a function of the number of cycles performed at 60° C. as described in Example 3.
    •  DETAILED DESCRIPTION
  • The present application describes electrolyte compositions comprising specific concentration and ratio of two lithium salts, a solvent (that may be a mixture of solvents) and an electrolytic additive. More specifically, the electrolyte composition comprises lithium hexafluorophosphate (LiPF6), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate (LiTDI), at least one solvent, and at least one electrolytic additive. The electrolyte composition as described herein comprises:
      • a total concentration of lithium hexafluorophosphate and of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate of less than or equal to 1 mol/L relative to the total volume of composition (i.e., [LiPF6]+[LiTDI]≤1 mol/L); and
      • a lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentration of less than or equal to 0.3 mol/L relative to the total volume of composition (i.e., 0<[LiTDI]≤0.3 mol/L).
  • For example, the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate content is less than or equal to 0.25 mol/L, or less than or equal to 0.2 mol/L, particularly less than or equal to 0.15 mol/L, or less than or equal to 0.1 mol/L, preferably less than or equal to 0.08 mol/L, preferably less than or equal to 0.05 mol/L, relative to the total volume of composition.
  • The lithium hexafluorophosphate concentration in the electrolyte composition may be greater than or equal to 0.80 mol/L and less than 1 mol/L, preferably comprised between 0.80 and less than 1 mol/L, particularly between 0.90 and 0.99 mol/L, and for example comprised between 0.95 mol/L and 0.99 mol/L, relative to the total volume of composition.
  • Examples of lithium hexafluorophosphate and lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentrations in the electrolyte composition comprise:
      • 0.99 mol/L of LiPF6 and 0.01 mol/L of LiTDI;
      • 0.98 mol/L of LiPF6 and 0.02 mol/L of LiTDI;
      • 0.97 mol/L of LiPF6 and 0.03 mol/L of LiTDI;
      • 0.96 mol/L of LiPF6 and 0.04 mol/L of LiTDI;
      • 0.95 mol/L of LiPF6 and 0.05 mol/L of LiTDI;
      • 0.90 mol/L of LiPF6 and 0.1 mol/L of LiTDI;
      • 0.80 mol/L of LiPF6 and 0.2 mol/L of LiTDI; and
      • 0.7 mol/L of LiPF6 and 0.3 mol/L of LiTDI.
  • According to a preferred embodiment, the electrolyte composition as described in the present application comprises 0.95 mol/L of LiPF6 and 0.05 mol/L of LiTDI, relative to the total volume of composition.
  • According to one embodiment, the solvent is non aqueous (organic). For example, the composition solvent may be selected from the group consisting of ethers, carbonic acid esters, cyclic carbonate esters, aliphatic carboxylic acid esters, aromatic carboxylic acid esters, phosphoric acid esters, sulfite esters, nitriles, amides, alcohols, sulfoxides, sulfolane, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1,H)-pyrimidinone, 3-methyl-2-oxazolidinone, or one of their mixtures.
  • Among ethers, mention may be made of linear or cyclic ethers such as, for example, dimethoxyethane (DME), methyl ethers of oligoethylene glycols of 2 to 5 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and their mixtures.
  • Among nitriles, mention may be made, for example, of acetonitrile, pyruvonitrile, propionitrile, methoxypropionitrile, dimethylaminopropionitrile, butyronitrile, isobutyronitrile, valeronitrile, pivalonitrile, isovaleronitrile, glutaronitrile, methoxyglutaronitrile, 2-methylglutaronitrile, 3-methylglutaronitrile, adiponitrile, malononitrile, and their mixtures.
  • Examples of solvents also include those selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate, methyl phenyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, and their mixtures. The solvent may also be selected from ethylene carbonate (EC-CAS N° 96-49-1), diethyl carbonate (DEC-CAS N° 105-58-8), and their mixtures. Preferably, the solvent is an ethylene carbonate:diethyl carbonate mixture in a ratio of between 1:99 and 99:1, preferably between 10:90 and 90:10, more preferably between 40:60 and 60:40.
  • Examples of electrolytic additive include fluoroethylene carbonate (FEC), vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, allyl ethyl carbonate, vinyl acetate, divinyl adipate, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonates, vinyl containing silane compounds, 2-cyanofurane and their mixtures, the electrolytic additive preferably being fluoroethylene carbonate (FEC). The electrolytic additive content may be comprised between 0.1% and 9%, preferably between 0.5% and 4%, by weight relative to the combined “solvent(s)+additive” total weight. Particularly, the electrolytic additive content in the electrolyte composition is less than or equal to 2% by weight relative to the combined “solvent(s)+additive” total weight.
  • According to an embodiment, the present electrolyte composition is selected from one of the following compositions (LiPF6 and LiTDI concentrations being expressed relative to the total composition volume and the additive content relative to the combined “solvent(s)+additive” total weight):
      • i. 0.99 mol/L of LiPF6 and 0.01 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • ii. 0.98 mol/L of LiPF6 and 0.02 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • iii. 0.97 mol/L of LiPF6 and 0.03 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • iv. 0.96 mol/L of LiPF6 and 0.04 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • v. 0.95 mol/L of LiPF6 and 0.05 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • vi. 0.90 mol/L of LiPF6 and 0.1 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • vii. 0.80 mol/L of LiPF6 and 0.2 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent; and
      • viii. 0.7 mol/L of LiPF6 and 0.3 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an
  • EC/DEC mixture as solvent.
  • The electrolyte composition may be prepared by dissolving, preferably with stirring, the salts in the appropriate proportions of solvent(s) comprising the electrolytic additive. Alternatively, the electrolyte composition may be prepared by dissolving, preferably with stirring, the salts and the electrolytic additive in appropriate proportions of solvent(s).
  • The use of an electrolyte composition of the present application in a Li-ion battery is also contemplated, in particular in a temperature range of higher than or equal to 25° C., preferably of between 25° C. and 65° C., advantageously between 40° C. and 60° C. For example, use is made in mobile devices, for instance mobile phones, cameras, tablets or laptops, in electric vehicles, or for the storage of renewable energy.
  • According to another aspect, the present application thus also relates to an electrochemical cell comprising a negative electrode, a positive electrode, and an electrolyte composition as defined herein, interposed between the negative electrode and the positive electrode. The electrochemical cell may also further comprise a separator in which the electrolyte composition of the present application is impregnated.
  • The present application also contemplates a battery comprising at least one electrochemical cell defined in this application. When the battery comprises several of these electrochemical cells, said cells can be assembled serially and/or in parallel.
  • In the context of the present application, by negative electrode is meant the electrode which acts as anode, when the battery delivers current (i.e. when in discharge process) and which acts as cathode when the battery is in charging process. The negative electrode typically comprises an electrochemically active material, optionally an electronically conductive material, and optionally a binder. The term “electrochemically active material” means a material capable of reversibly inserting ions, without irreversibly damaging their structure. By “electronically conductive material” is meant a material capable of conducting electrons.
  • For example, the battery negative electrode may comprise as electrochemically active material, graphite, carbon fibers, carbon black, or a mixture thereof, the negative electrode preferably comprising graphite. The negative electrode may also comprise lithium, which may then consist of a metallic lithium film or of an alloy comprising lithium. A negative electrode example comprises an active lithium film prepared by rolling a lithium foil between rolls.
  • In the context of the present application, by positive electrode is meant the electrode which acts as a cathode when the battery delivers current (i.e. when in discharge process) and which acts as the anode when the battery is in charging process. The positive electrode usually comprises an electrochemically active material, optionally an electronically conductive material, and optionally a binder.
  • The electrochemical cell's positive electrode may comprise an electrochemically active material selected from LiCoO2, LiFePO4 (LFP), LiMnxCoyNizO2 (NMC, with x+y+z=1), LiFePO4F, LiFeSO4F, LiNiCoAlO2 and their mixtures.
  • In addition to the electrochemically active material, the positive electrode material may also comprise an electronically conductive material such as a carbon source, including, for example, carbon black, Ketjen® carbon, Shawinigan carbon, graphite, graphene, carbon nanotubes, carbon fibers (such as vapor grown carbon fibers (VGCF)), non-powdery carbon obtained by carbonizing an organic precursor, or a combination of at least two thereof. Other additives may also be present in the positive electrode material, such as lithium salts or inorganic particles of ceramic or glass type, or other compatible active materials (for example, sulfur).
  • The positive electrode material may also comprise a binder. Non-limiting examples of binders include linear, branched and/or crosslinked polyether polymer binders (e.g., polymers based on poly(ethylene oxide) (PEO), or poly(propylene oxide) (PPO) or a mixture of both (or a EO/PO copolymer), and optionally comprising crosslinkable units), water soluble binders (such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber)), or fluorinated polymer type binders (such as PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and their combinations). Some binders, such as those soluble in water, may also include an additive such as CMC (carboxymethylcellulose).
  • According to one embodiment, the electrochemical cell comprises a negative electrode containing graphite, a positive electrode containing LiMnxCoyNizO2 (NMC, with x+y+z=1), and an electrolyte composition as herein defined, interposed between the negative electrode and positive electrode, the composition being preferably selected from any of the following compositions (LiPF6 and LiTDI concentrations being expressed relative to the total volume of composition and the additive content expressed relative to the “solvent(s)+additive” total combined weight):
      • i. 0.99 mol/L of LiPF6 and 0.01 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • ii. 0.98 mol/L of LiPF6 and 0.02 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • iii. 0.97 mol/L of LiPF6 and 0.03 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • iv. 0.96 mol/L of LiPF6 and 0.04 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • v. 0.95 mol/L of LiPF6 and 0.05 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • vi. 0.90 mol/L of LiPF6 and 0.1 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • vii. 0.80 mol/L of LiPF6 and 0.2 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent; and
      • viii. 0.7 mol/L of LiPF6 and 0.3 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent.
  • According to another embodiment, the electrochemical cell comprises a negative electrode containing graphite, a positive electrode containing LiFePO4 (LFP) and a mixture of carbon black with carbon fibers and/or carbon nanotubes, and an electrolyte composition as defined herein, interposed between the negative electrode and positive electrode, the composition preferably being selected from any of the following compositions (LiPF6 and LiTDI concentrations being expressed relative to the total volume of composition and the additive content expressed relative to the “solvent(s)+additive” total combined weight):
      • i. 0.99 mol/L of LiPF6 and 0.01 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • ii. 0.98 mol/L of LiPF6 and 0.02 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • iii. 0.97 mol/L of LiPF6 and 0.03 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • iv. 0.96 mol/L of LiPF6 and 0.04 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • v. 0.95 mol/L of LiPF6 and 0.05 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • vi. 0.90 mol/L of LiPF6 and 0.1 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent;
      • vii. 0.80 mol/L of LiPF6 and 0.2 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent; and
      • viii. 0.7 mol/L of LiPF6 and 0.3 mol/L of LiTDI, FEC as electrolytic additive (particularly at a concentration less than or equal to 2% by weight), and an EC/DEC mixture as solvent.
  • For example, the electrochemical cell as described herein may have a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage Vlow between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 45° C., and at a charge and discharge C rate. In particular, the voltage Vlow may be of 2.8 volts and the voltage Vhigh is of 4.2 volts, the positive electrode preferably comprising LiCoO2, LiMnxCoyNizO2 (with x+y+z=1), LiFePO4F, LiFeSO4F, LiNiCoAlO2 or their mixtures.
  • According to another embodiment, the electrochemical cell as described herein may have a capacity retention greater than or equal to 80% after at least 60 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage Vlow between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 60° C., and at a charge and discharge C/4 rate, charging being optionally followed by the application of a constant voltage of 4.2V for 1 h. In particular, the voltage Vlow is of 2.8 volts and the voltage Vhigh is of 4.2 volts, the positive electrode preferably being selected from the group consisting of LiCoO2, LiMnxCoyNizO2 (with x+y+z=1), LiFePO4F, LiFeSO4F, LiNiCoAlO2 and mixtures thereof. According to one example, charging is followed by the application of a constant voltage as described.
  • In another example, the electrochemical cell of the present technology has a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage Vlow of between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh of between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 25° C., and at a charge and discharge rate of C, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO4. Particularly, the voltage Vlow may be equal to 2 volts and the voltage Vhigh is of 4 volts. According to an example, charging is followed by the application of a constant voltage as described.
  • The electrochemical cell of the present technology may also have a capacity retention greater than or equal to 80% after at least 200 charge/discharge cycles relative to the first cycle, for a charge comprised between a voltage Vlow between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 40° C., and at a charge and discharge C rate, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO4. Particularly, the voltage Vlow is equal to 2 volts and the voltage Vhigh is of 4 volts. According to an example, charging is followed by the application of a constant voltage as described.
  • The electrochemical cell of the present technology may have a capacity retention greater than or equal to 80% after at least 100 charge/discharge cycles relative to the first cycle, for a charge comprised between a voltage Vlow between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 60° C., and at a charge and discharge C rate, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO4. Particularly, the voltage Vlow is equal to 2 volts and the voltage Vhigh is of 4 volts. According to an example, charging is followed by the application of a constant voltage as described.
  • The present application also relates to the use of the electrolyte composition as described herein for:
      • improving a Li-ion battery life; and/or
      • improving a Li-ion battery cycling stability; and/or
      • reducing a Li-ion battery irreversible capacity;
  • especially in a temperature range above or equal to 25° C., preferably between 25° C. and 65° C., advantageously between 40° C. and 60° C.
  • Another aspect relates to the use of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate in an electrolyte composition comprising lithium hexafluorophosphate and at least one electrolytic additive for:
      • improving a Li-ion battery life; and/or
      • improving a Li-ion battery cycling stability; and/or
      • reducing a Li-ion battery irreversible capacity;
  • especially in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C.;
  • the composition being such that:
      • the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate and lithium hexafluorophosphate total concentration is less than or equal to 1 mol/L; and
      • the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentration is less than or equal to 0.3 mol/L, preferably less than or equal to 0.05 mol/L.
  • According to an example, the use of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate in an electrolyte composition as herein described and comprising lithium hexafluorophosphate and at least one electrolytic additive, makes it possible to improve the life duration of a Li-ion battery; and/or to improve the stability to cycling of a Li-ion battery; and/or to reduce the irreversible capacity of a Li-ion battery. This improvement may occur especially in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C. For instance, the presence of LiTDI in the electrolyte composition makes it possible to increase the life of the battery (80% loss of initial capacity) by at least 1.5-fold, or at least 2-fold, compared to a battery without LiTDI used in the same conditions. According to another example, the battery life is multiplied by at least 1.5, or at least 2, or multiplied by a number within the range of from 1.5 to 8, or from 2 to 7.
  • It is understood that measurable or quantifiable values, such as concentrations, volumes, etc. mentioned in this application must be interpreted taking into account the limitations of the analysis method and the uncertainty inherent to the instrument used.
  • All embodiments and alternatives described above can be combined with each other. In particular, the various embodiments and alternatives of the various composition elements can be combined with each other, as well as for the use of said composition.
  • For the purposes of this document, “between x and y”, or “from x to y”, means an interval in which the x and y terminals are included. For example, the range “between 1 and 4%” namely includes the values 1 and 4%.
  • The following examples are for illustrative purposes and should not be interpreted as limiting the scope of the invention as described.
    • EXAMPLES Example 1
  • The first example carried out consists in dissolving, at room temperature, a salt mixture containing LiPF6 and LiTDI (or LiPF6 alone as a reference) at a total concentration of 1 mol/L, in a mixture of three carbonates: ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in EC/DEC/FEC weight proportions of: 36.84%, 61.16% and 2% respectively.
  • Four mixtures were thus prepared in this example in the following proportions:
      • 1 mol/L of LiPF6
      • 0.95 mol/L of LiPF6 and 0.05 mol/L of LiTDI
      • 0.9 mol/L of LiPF6 and 0.1 mol/L of LiTDI
      • 0.8 mol/L of LiPF6 and 0.2 mol/L of LiTDI
  • These mixtures were electrochemically evaluated in lithium-ion pouch-cells of 11.5mAh capacity, with NMC and graphite as cathode and anode materials respectively. The system's cycling terminals are of 2.8-4.2V. After a slow rate (C/24) formation at room temperature, the mixtures were evaluated at 45° C. with a C charge and discharge. Results obtained are presented in FIG. 1. If the end of life of a battery is considered to be when it has lost 80% of its initial capacity, the addition of LiTDI can multiply by 2.5 to 3.3 the life of the battery. The use of LiTDI at a content of only 0.05 mol/L makes it possible to carry out more than 600 cycles at the battery end of life.
    • Example 2
  • The second example carried out consists in dissolving at room temperature a salt mixture containing LiPF6 and LiTDI (or LiPF6 alone for the reference) at a total concentration of 1 mol/L, in a mixture of three carbonates: ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in weight proportions of 36.84%, 61.16% and 2% respectively.
  • The following four mixtures were prepared:
      • 1 mol/L of LiPF6
      • 0.95 mol/L of LiPF6 and 0.05% mol/L of LiTDI
      • 0.9 mol/L of LiPF6 and 0.1 mol/L of LiTDI
      • 0.7 mol/L of LiPF6 and 0.3 mol/L of LiTDI
  • These mixtures were electrochemically evaluated in lithium-ion pouch-cells of 11.5 mAh capacity, with NMC and graphite as cathode and anode materials respectively. The system's cycling terminals are 2.8-4.2V. After a slow rate (C/24) formation at room temperature, the mixtures were evaluated at 60° C. with a C/4 charge followed by application of a constant voltage at 4.2 V for 1 hour, and then a C/4 discharge. FIG. 2 shows the results obtained. If the end of life of a battery is considered to be when it has lost 80% of its initial capacity, the addition of LiTDI can multiply by 3 the life of the battery.
    • Example 3
  • A salt mixture containing LiPF6 and LiTDI (or LiPF6 alone for the reference) is dissolved at a total concentration of 1 mol/L in a mixture of three carbonates: ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in weight proportions of 36.84%, 61.16% and 2% respectively.
  • Three mixtures were prepared in this example in the following proportions:
      • 1 mol/L of LiPF6
      • 0.95 mol/L of LiPF6 and 0.05 mol/L of LiTDI
      • 0.8 mol/L of LiPF6 and 0.2 mol/L of LiTDI
  • These mixtures were electrochemically evaluated in lithium-ion pouch-cells of 10 mAh capacity, with LFP and graphite as cathode and anode materials respectively. For the cathode, the electronic conductor used is a mixture of carbon black with either carbon fibers or nanotubes. The system's cycling terminals are 2-4V. After a slow rate (C/24) formation at room temperature, the mixtures were evaluated at 25, 40 and 60° C. with a C charge followed by application of a constant voltage at 4 V for 30 minutes, and then a C discharge. Results obtained are presented in FIGS. 3, 4 and 5 respectively (results shown for cells comprising 0.05 mol/L of LiTDI).
  • If the end of life of a battery is considered to be when it has lost 80% of its initial capacity, at 25° C. the addition of LiTDI at only 0.05 mol/L makes it possible to multiply by 3.2 the life of the battery with carbon nanotubes as electronic conductor and by 2.5 with the carbon fibers. The improvement in cyclability is more pronounced in the presence of carbon nanotubes where the battery life is increased by 4.2 times by adding 0.2 mol/L of LiTDI. At 40 and 60° C., the addition of 0.05 mol/L of LiTDI is sufficient to improve the cycle life of a few tens of cycles, whether with VGCF or CNT electronic conductors.
  • In summary, the effect of the LiTDI lithium salt on battery life has been demonstrated in the various series of electrochemical tests carried out on 10 mAh or 11.5 mAh capacity pouch-cells. The systems studied are LFP (with carbon black and CNT or VGCF)/graphite and NMC/graphite. Tests were carried out between 25° C. and 60° C., with or without applying a constant voltage after charging.
  • It has been shown that the addition of LiTDI (from 0.05 mol/L) makes it possible to significantly improve battery life. Without wishing to be bound by theory, it seems that the presence of LiTDI could allow to capture water molecules and prevent HF formation that occurs when LiPF6 reacts with traces of moisture which may be contained in the cathodes, anodes, separator, solvent, packaging, etc. Unlike LiPF6, LiTDI does not seem to be affected by the presence of moisture and can increase the life of the battery even at low concentration.
  • The series of tests carried out also demonstrates the good resistance in abusive cycling (application of constant voltage at the end of charging) of the tested electrolytes when containing LiTDI (from 0.05 mol/L). The tests carried out at room temperature on the LFP/graphite system further demonstrate the resistance to abusive cycling (no temperature effect) of electrolytes containing LiTDI, whether with VGCF or CNT type electronic conductors; the life of the battery being multiplied by 2.5 or 3.2 times.
  • Several modifications could be made to any of the above described embodiments without departing from the scope of the present invention as contemplated. Any references, patents or scientific literature documents referred to in the present application are incorporated herein by reference in their entirety and for all purposes.

Claims (23)

1. Electrolyte composition comprising lithium hexafluorophosphate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate, at least one solvent, and at least one electrolytic additive, said composition comprising:
a total concentration of lithium hexafluorophosphate and lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate less than or equal to 1 mol/L relative to the total volume of the composition, and
a lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentration less than or equal to 0.3 mol/L relative to the total volume of the composition.
2. Composition according to claim 1, wherein the content of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate is less than or equal to 0.2 mol/L, in particular less than or equal to 0.1 mol/L, preferably less than or equal to 0.08 mol/L, more preferably less than or equal to 0.05 mol/L, relative to the total volume of the composition.
3. Composition according to claim 1, wherein the solvent is selected from the group consisting of ethers, carbonic acid esters, cyclic carbonate esters, aliphatic carboxylic acid esters, aromatic carboxylic acid esters, phosphoric acid esters, sulfite esters, nitriles, amides, alcohols, sulfoxides, sulfolane, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1,H)-pyrimidinone, 3-methyl-2-oxazolidinone, and mixtures thereof.
4. Composition according to claim 3, wherein the solvent is selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate, methyl phenyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, and mixtures thereof.
5. Composition according to claim 4, wherein the solvent is selected from the group consisting of ethylene carbonate, diethyl carbonate, and mixtures thereof.
6. Composition according to claim 1, wherein the electrolytic additive is selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, allyl ethyl carbonate, vinyl acetate, divinyl adipate, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonates, vinyl containing silane compounds, 2-cyanofurane and mixtures thereof, the electrolytic additive preferably being fluoroethylene carbonate.
7. Composition according to claim 1 wherein the content of electrolytic additive is comprised between 0.1% and 9%, preferably between 0.5% and 4% by weight relative to the “solvent(s)+additive” total combined weight.
8. Composition according to claim 1, wherein the concentration of lithium hexafluorophosphate is greater than or equal to 0.80 mol/L and less than 1 mol/L, preferably comprised between 0.80 and less than 1 mol/L, particularly between 0.90 and 0.99 mol/L, and for example comprised between 0.95 mol/L and 0.99 mol/L, relative to the total volume of the composition.
9. Composition according to claim 1, wherein the lithium hexafluorophosphate concentration is of 0.95 mol/L, and the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentration is of 0.05 mol/L, relative to the total volume of the composition.
10. Use of a composition according to claim 1, in a Li-ion battery, particularly in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C.
11. Use according to claim 10, in mobile devices, for instance mobile phones, cameras, tablets or laptops, in electric vehicles, or in the storage of renewable energy.
12. Use of a composition according to claim 1, for:
improving a Li-ion battery life; and/or
improving a Li-ion battery cycling stability; and/or
reducing a Li-ion battery irreversible capacity;
particularly in a temperature range above or equal to 25° C., preferably comprised between 25° C. and 65° C., advantageously between 40° C. and 60° C.
13. Electrochemical cell comprising a negative electrode, a positive electrode, and an electrolyte composition as defined in claim 1, interposed between the negative electrode and the positive electrode.
14. Electrochemical cell according to claim 13, wherein the negative electrode comprises graphite, carbon fibers, carbon black, lithium, or a mixture thereof, the negative electrode preferably comprising graphite.
15. Electrochemical cell according to claim 13, wherein the positive electrode comprises LiCoO2, LiFePO4, LiMnxCoyNizO2 (where x+y+z=1), LiFePO4F, LiFeSO4F, LiNiCoAlO2 or a mixture thereof, the positive electrode preferably comprising LiFePO4 or LiMnxCoyNizO2 (where x+y+z=1).
16. Electrochemical cell according to claim 13, having a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage Vlow between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 25° C., and at a charge and discharge rate of C.
17. Electrochemical cell according to claim 16, wherein the voltage Vlow is equal to 2.8 volts and the voltage Vhigh is equal to 4.2 volts, the positive electrode preferably comprising LiCoO2, LiMnxCoyNizO2(with x+y+z=1), LiFePO4F, LiFeSO4F, LiNiCoAlO2 or their mixtures.
18. Electrochemical cell according to claim 16, having a capacity retention greater than or equal to 80% after at least 500 charge/discharge cycles compared to the first cycle, for a charge comprised between a voltage Vlow between 2.0 and 3.0 volts versus Li+/Li0, and a voltage Vhigh between 3.8 and 4.2 volts versus Li+/Li0, at a temperature of 25° C., and at a charge and discharge rate of C, charging being optionally followed by the application of a constant voltage of 4V during 30 minutes, the positive electrode preferably comprising LiFePO4.
19. Electrochemical cell according to claim 18, wherein the voltage Vlow is equal to 2 volts and the voltage Vhigh is equal to 4 volts.
20. Electrochemical cell according to claim 18, charging being followed by the application of a constant voltage of 4V for 30 minutes.
21. Electrochemical cell according to claim 18, charging not being followed by the application of a constant voltage of 4V for 30 minutes and the capacity retention being greater than or equal to 80% after at least 800 cycles.
22. Battery comprising at least one electrochemical cell according to claim 13.
23. Use of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate in an electrolyte composition comprising lithium hexafluorophosphate and at least one electrolytic additive for:
improving a Li-ion battery life; and/or
improving a Li-ion battery cycling stability; and/or
reducing a Li-ion battery irreversible capacity;
especially in a temperature range above or equal to 25° C., preferably between 25° C. and 65° C., advantageously between 40° C. and 60° C.;
the composition being such that:
the total concentration of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate and lithium hexafluorophosphate is less than or equal to 1 mol/L relative to the total volume of the composition; and
the lithium 4,5-dicyano-2-(trifluoromethyl)imidazolate concentration is less than or equal to 0.3 mol/L, preferably less than or equal to 0.05 mol/L, relative to the total volume of the composition.
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